The four ventricles of the human brain are interconnected cavities that produce and circulate cerebral-spinal fluid (CSF). Procedures involving ventriculostomy, i.e., placement of a catheter into the ventricular system of the brain, form a major part of a neurosurgeon's clinical practice. General areas of application of ventricular catheter placement include intracranial pressure monitoring (ICP), draining or shunting of CSF and the instillation of pharmacological therapeutic agents.
Intracranial pressure monitoring, i.e., a monitoring of ventricular pressure, is critical to the management of patients after severe head trauma, fulminant meningitis, Reyes' syndrome, encephalitis, stroke, cerebral hemorrhage, or subarachnoid hemorrhage producing stupor or coma. However, the ventricles are usually compressed after head trauma and thus technically difficult to cannulate for ICP monitoring. Accordingly, subarachnoid pressure monitoring, which is not as true a measure of cerebral pressure as intraventricular pressure monitoring, is generally used.
CSF drainage is essential for patients with congenital or acquired hydrocephalus. This procedure, which can only be performed with an intraventricular catheter, is a life-preserving step, because it can immediately reduce intracranial pressure. The ventricular catheter used to drain cerebral-spinal fluid is connected to a peripheral subcutaneous drainage system, i.e., to the peritoneal cavity or systemic circulation via the heart. In hydrocephalus, the ventricles are enlarged and are an easier target for cannulation. However, recent reports in neurosurgical literature indicate that suboptimal placement in dilated ventricles can subsequently produce catheter obstruction when the ventricles are decompressed and become smaller, thus emphasizing the need for accurate placement.
Catheter placement in cerebral ventricles is widely performed on patients with carcinomatous and fungal meningitis for the administration of well-known antineoplastic and antifungal chemotherapetuic agents, respectively. Invariably, the ventricles in these patients are small or normal sized and difficult to cannulate.
Standard procedures for ventricular catherization are disclosed in the textbook literature. See, for example, Neurosurgery, edited by Robert H. Wilkins and Setti S. Rengachary, Section A, Chapter 13, Techniques of Ventricular Puncture (McGraw Hill 1984).
The most frequently chosen site for ventricular catheterization is the coronal region. In most cases, a catheter is inserted in the anterior horn of the lateral ventricle through an orifice or burr hole drilled just anterior to the coronal suture in the midpupillary line of the cranium, i.e., in the frontal bone over the ventricle. This is known in the field as Kocher's point. The burr hole, only slightly larger than the diameter of the selected catheter to insure a snug fit and provide a seal against CSF leakage, is placed approximately 1 cm. anterior to the coronal suture, approximately 10 to 12 cm. above the nasion, and approximately 2 to 3 cm. from the midline over the nondominant hemisphere. After the burr hole is made, the dura and underlying pia-arachnoid are opened and coagulated, for example, with a fine-tipped blade, after cauterizing the dural surface.
The lateral ventricles of the human brain form an arc parallel to the arc of the cranium, i.e., the contour of the lateral ventricles parallels the arc of the surface of the skull. Thus, a catheter guided perpendicular to the cranial surface at the point of entry into the cranium will enter the ventricular system. Specifically, any line penetrating a burr hole in the surface of the skull at a 90.degree. angle also bisects the lateral ventricle.
Various methods have been utilized in the prior art in an attempt to ensure the correct placement of a catheter device in the patient's cerebral ventrical. One such method involves the use of a pre-measured catheter having a stylet which may be introduced and directed freehand through the burr hole, approximately in the coronal plane, and angled towards the medial canthus of the ipsilateral eye, using external landmarks such as the inner canthus of the eye in the frontal plane and a point just in front of the external auditory meastus in the lateral plane as guided to placement. CSF should flow freely from the catheter tip at a depth of approximately 4 to 5 cm. from the interior cranial surface.
A distinctive "give", or release of opposition, can often be felt when the ventricle is penetrated. Pressure should be measured at this point, however, since an artificially low value will be obtained even if small amounts of fluid are lost. Then, after removal of the stylet from the catheter, advancement another 1 cm. or so should insure placement in the frontal horn at a depth of about 5 to 6 cm. from the external table of the skull, care being taken that CSF continues to flow.
Intraoperative fluoroscopy and air ventriculography, well known techniques in the art, have been used to confirm freehand catheter placement. While these procedures can be helpful in placing the catheter if the ventricles are small, they also add to the complexity of the overall procedure.
Aside from the cost and time constraints of such radiographic confirmation of catheter placement, many published reports of postoperative studies have revealed misplacement of catheter tips in cerebral matter or subarachnoid space. This misplacement results in increased neurological morbidity and the need for additional operation time. Moreover, multiple passes of the catheter into cerebral matter are quite common before the ventricles are properly penetrated. Finally, the anxiety a neurosurgeon experiences when trying to place a catheter by freehand into the ventricular system makes first pass success that much more difficult and further increases the risks involved in the procedure.
A more recently developed procedure to ensure correct catheter placement was disclosed and claimed by one of the present applicants in U.S. Pat. No. 4,613,324, issued Sept. 23, 1986. The disclosure of that patent is therefore specifically incorporated herein by reference. The apparatus comprises a guide assembly which, when positioned over an orifice drilled in the cranium above the anterior horn of the lateral ventricle, guides a catheter and obdurator through the orifice and into the lateral ventricle at an angle normal to an imaginary plane formed by a tangent to the cranium at the orifice.
The method of utilizing the claimed device comprises providing an orifice in the cranium just anterior to the coronal suture in a midpupillary line of the cranium and inserting a ventricular catheter containing an obdurator through the orifice towards a lateral ventricle, wherein the catheter containing the obdurator is guided through the orifice, by means of a novel guide assembly, at an angle normal to an imaginary plane formed by a tangent to the cranium at the orifice.
Although the procedures described above may be effective in positioning a catheter in a patient's lateral ventricle once a correctly aligned burr hole has been prepared for its passage, there is no art which the applicants are aware of which ensures that the initial perforation in the patient's cranium can be prepared and aligned so as to extend through the skull at an angle of substantially 90.degree. to the surface thereof.
This orientation is required for proper placement of the catheter within the ventricular portion of the patient's brain since, if the burr hole deviates by more than about 7 degrees from the perpendicular to a plane tangent to the point on the cranium where the catheter is inserted, the catheter will be directed away from the ventricular region and into other areas of the organ not conducive to the intended purposes of the apparatus disclosed. Thus, aligning the burr hole in such a precise manner greatly simplifies the subsequent task of correctly aligning the catheter within the ventricular cavity.
The difficulty in obtaining such a precisely aligned burr hole has thus led to the search for a rapid, simple, inexpensive and accurate method and apparatus for perforating the patient's cranium at an angle of substantially 90.degree. to the surface prior to the insertion of a catheter into the patient's cerebral ventricle.